1. Field of the Invention
The present invention relates to a developing device formed with a housing that houses developing agent and a developing chamber that houses a developing-agent holding member.
2. Related Art
There has been provided a conventional developing device that is used in a leaser printer. Such a developing device is formed with a toner hopper and a developing chamber. The toner hopper houses non-magnetic single-component toner, for example. Positioned inside the developing chamber are a developing roller, a supply roller, a regulation blade, and the like. An opening is formed between the toner hopper and the developing chamber for allowing the toner to freely move between the toner hopper and the developing chamber.
In this configuration, toner is supplied from the toner hopper into the developing chamber as needed, and transported by the supply roller onto the developing roller. Some of the toner on the developing roller is transferred onto a photosensitive member for development, and the remaining is left on the developing roller. For example, when only a small amount of toner is used for development, relatively large amount of toner will remain on the developing roller.
Thus remained toner is collected into the developing chamber. Because toner is freely movable between the developing chamber and the toner hopper through the opening as described above, thus collected toner can return into the toner hopper. When toner repeatedly circulates between the developing roller and the developing chamber or the toner hopper in this manner, the toner will be gradually degraded. As a result, a leaser printer will provide only poor quality images after a long period of use because of the degraded toner, even if the leaser printer can provide a high quality image at the beginning of use.
In order to solve the above problems, Japanese Patent Application Publication No. SHO-60-59375 has proposed a developing device capable of preventing degraded toner from entering a toner hopper. Specifically, the developing device is formed with a vertically extending toner hopper, inside of which is partitioned into three spaces by partitioning members with respect to the vertical direction. When toner empty condition of a developing chamber is detected, the partitioning members are opened one by one, so the toner stored inside the space falls and supplied into the developing chamber by gravity. Because the toner will not enter the toner hopper against the gravity, a high quality image is provided stably.